The present invention relates to hybrid power systems, more particularly to improving efficiencies of hybrid power systems involving renewable energy such as solar power.
The United States Navy is at the forefront of hybrid power systems design. Navy data demonstrates the need for technology development in various respects, including reduction of liquid fuel consumption and of the dangers and costs of logistics resupply to forward-deployed locations. The Navy is considering more efficient ways of supporting forward-deployed power requirements.
A current approach to supporting ground-based power requirements of the armed services involves deployment of designated electric diesel generators with an equipment set required to provide a specific capability. Depending on many factors, it is incumbent upon the utilities community to determine which generator will support the peak power requirements of a given piece of equipment or capability. Because of inconsistencies in equipment sets, the drastic diurnal and seasonal power fluctuation inherent to the primary energy consumers, and a limited number of fielded generator sizes, properly sizing a generator to its load becomes very difficult, often resulting in underutilized generators.
Navy statistical evidence demonstrates that generators are frequently operated at less than 50% of their rated capacity. In order to achieve established fuel consumption requirements, liquid fuel needs to be continually used at peak efficiency. FIG. 1 illustrates that current program-of-record generators used by the Navy achieve maximum energy production per gallon of fuel at their peak load.
Despite the difficulty associated with predicting peak load for any given system, once loads are employed, they become very predictable from day to day. Two types of loads are typically supported with generators, those that are dedicated or standalone systems, and those that are made up of many components that provide a capability set.
Dedicated loads are very predictable but make up a small percentage of total power consumed by our armed services. Capability sets such as Combat Operations Centers make up the majority of the loads on the battle field but are inconsistently deployed and have great diurnal and seasonal power fluctuation due to fact that over 70% of their power demand is made up by environmental control systems. Despite drastic daily and seasonal fluctuation, typical loads are very consistent in daily energy consumption, making them very predictable. FIG. 2 illustrates the power fluctuation of a large Combat Operation Center with cyclic diurnal behavior.
Due to the many factors that make rightsizing generators to their loads difficult, it has become increasingly apparent that a materiel solution needs to be put in place to achieve Navy/Marine Corps goals for energy savings and increased sustainability on the battlefield. Additional goals set by the Navy have defined specific fuel consumption requirements for a future program-of-record family of hybrid power systems referred to as the Mobile Electric Hybrid Power Systems (MEHPS). These requirements begin to shape what a hybrid power system will look like on the battlefield. Hybrid power systems are typically made up of multiple sources of power generation, energy storage, power electronics, and a control system.
Tri principle, the basic function of a hybrid power system (e.g., a photovoltaic diesel-generator hybrid power system) solves the problem of rightsizing a fuel burning generator to its load, as a properly designed hybrid power system uses available energy storage to load a generator at peak efficiency whenever the generator is running. When the generator is not running, the energy storage and any available “free” or renewable energy will be used to support the load, resulting in efficient consumption of logistics fuel and reduced generator maintenance. Many of the requirements set forth by the procurement offices drive aspects of systems such as energy storage size and the amount of renewable energy required meeting fuel savings goals. In order to meet the MEHPS requirements, renewable energy must be used to supplement a fuel burning generator.
Key performance parameters (KPPs) such as cost, weight, footprint, and setup time heavily drive the maximum capacity of components critical to energy production. Because of these limitations on component size, fuel consumption of a Navy tactical hybrid power system is influenced heavily at low loads by renewable energy and less so at loads between 50 and 100% of the system capacity. Because statistical analysis shows that tactical power systems are often operated at low loads, hybrid power systems provide an operational and economic benefit where they are most typically used; however, significant inefficiencies have been identified in how current hybrid systems use their renewable components.
Current state-of-the-art control architectures for hybrid power systems use hard set points, which are intended to minimize fuel consumption while conservatively utilizing the various components of the system in an attempt to maximize system life. Conservative thresholds can often cause unintentional cyclic behavior of system components because of operating parameters that hover at or near set point thresholds. Additionally, current architectures are designed to a specific application or load profile, resulting in inefficient and inconsistent utilization of renewable resources, which is the most important contributor to reaching energy production goals set by the requirements community.
Hybrid power systems that utilize current control system architectures may be able to achieve specific requirement goals set by procurement offices; however, they will not be able to achieve efficient utilization of system resources consistently throughout the systems operating range. Current systems do not take full advantage of renewable sources, primarily because of: dominance struggles between power sources; unavailability of energy storage to sufficiently store renewable sources when the renewable sources are available; and, conservative set points that may drive fuel burning generators to start unnecessarily.